How much does a Mercedes E Class 400 d engine replacement cost in the UK-

Supply-only rebuilt OM656 engines range from £4,200 to £6,500 depending on condition. With specialist fitting, budget £4,600-£7,300 total. OM642.853/873 (E 350 d, 258 hp, 2016-2018): rebuilt £3,200-£4,800. OM656.929 (E 400 d, 340 hp, 2018-2023): rebuilt £4,200-£6,500. Labour adds £400-£800 depending on specialist location.

What are the signs of OM656 tandem pump failure in an E Class 400 d-

Intermittent limp mode that clears on restart, turbo actuator issues, and P0299E6 boost pressure codes are the classic signs. In severe cases, loss of braking assistance can occur. Intermittent power loss or limp mode, clearing on engine restart. P0299E6 error code (boost pressure too low). Juddering or clunky gear changes on longer journeys. Oil in vacuum lines (diagnostic check required).

Is it worth replacing the engine on an E Class 350 d or 400 d-

Yes, if the car is otherwise sound. W213 E 350 d examples command £15,000-£25,000 used, while E 400 d examples command £25,000-£40,000, making replacement viable. A quality rebuilt OM642 costs £3,200-£4,800 supply only. A quality rebuilt OM656 costs £4,200-£6,500 supply only. The OM656 is the most powerful diesel engine Mercedes ever produced for a series car. A replacement engine with warranty costs less than the depreciation on a newer car.

What causes the OM642 oil cooler seals to fail on E 350 d models-

The rubber seals harden with heat cycles and degrade over time, causing oil to leak into the engine Vee. This is the defining weakness of the OM642 V6 engine family. Seal failure typically occurs between 60,000-100,000 miles. Oil drips under the engine bay and a burning oil smell are the early warning signs. Oil cooler seal replacement at a specialist costs £700-£1,100. Later OM642 engines (2014+) have improved seals but can still fail.

What is the difference between the OM642 and OM656 engines in the E Class-

The OM642 is a 3.0-litre V6 diesel (2016-2018 E 350 d); the OM656 is a 3.0-litre straight-six diesel (2018-2023 E 400 d) - more powerful, more refined, and borrowed from the S-Class. OM642: V6 configuration, 258 hp, 620 Nm - proven but has oil cooler seal issues. OM656: straight-six configuration, 340 hp, 700 Nm - smoother, more powerful, but has tandem pump issues. The OM656 replaced the OM642 in the E-Class from 2018 onwards. Both are Euro 6 compliant with AdBlue emissions treatment.

How long does a Mercedes E Class 400 d engine last-

With proper maintenance and 8,000-10,000 mile oil changes, OM656 engines regularly reach 200,000+ miles. Some examples have exceeded 100,000 miles with proper servicing. OM656 straight-six is a modern, efficient design with robust bottom end. Tandem pump replacement at 40k-80k miles is a known requirement for early examples. Camshaft and rocker inspection at 80k-100k miles is recommended. Short oil change intervals (8k miles) are critical for longevity.

Mercedes E Class 350 / 400 d SPECIALISTS

Mercedes Benz E Class 350 d / 400 d Engine Replacement Compare Prices & Get Quotes

Get quotes today from trusted UK Mercedes Benz E Class 350 d and 400 d engine specialists. Compare prices on reconditioned, rebuilt and used OM642 V6 and OM656 straight-six diesel engines - supply & fit available nationwide.

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Mercedes Benz E Class 350 d / 400 d Engine

from£2,200 to £6,500

Usedfrom £1,800
Reconditionedfrom £2,500
Common codesOM642.853, OM642.873, OM656.929

Mercedes Benz e-class 350 d / 400 d Used Engine — OM642.853 / OM642.873

Mercedes Benz e-classUsed Engine — OM642.853 / OM642.873

Mercedes Benz e-class 350 d / 400 d Reconditioned Engine — OM642.853 / OM642.873

Mercedes Benz e-classReconditioned Engine — OM642.853 / OM642.873

Mercedes Benz e-class 350 d / 400 d Rebuilt Engine — OM642.853 / OM642.873

Mercedes Benz e-classRebuilt Engine — OM642.853 / OM642.873

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How it works

3 Simple Steps to Finding the Right Replacement Engine

Clear information first, then the right engine and specialist for your exact vehicle.

Variant History

Mercedes Benz E Class 350 d / 400 d Engine History & Specs at a Glance

The E 350 d and E 400 d badges represented Mercedes-Benz's flagship six-cylinder diesel offerings across the W213 E-Class generation. The E 350 d launched with the proven OM642 3.0-litre V6 diesel in 2016, before being replaced in 2018 by the E 400 d - powered by the all-new OM656 3.0-litre straight-six diesel, a more powerful and refined engine borrowed from the S-Class.

2016
W213 E 350 d launched with OM642 V6 diesel, 190 kW (258 hp), 620 Nm
2017
Mercedes temporarily suspended E 350 d sales in Germany due to NOx emissions compliance issues
2018
E 400 d introduced, replacing the E 350 d with the new OM656 3.0-litre straight-six diesel
**2018-2021** - E 400 d with OM656.929 producing 250 kW (340 hp), 700 Nm
2021
W213 facelift; E 400 d continues with revised OM656.929, now rated at 243 kW (330 hp) in some markets
2023
W214 generation launched; E-Class six-cylinder diesel offerings move to new engine architecture

Every engine fitted to the Mercedes E Class 350 d and 400 d is covered below, with UK rebuilt pricing and known failure points.

Engine Codes & Pricing

Mercedes Benz E Class 350 d / 400 d Engine Codes Specifications & Replacement Cost

Find your exact engine code, specs and UK replacement cost guide.

OM642.853 / OM642.873 — 3.0L V6 Diesel (2016-2018)

Power Output: 190 kW (258 hp) at 3,400 rpm
Torque: 620 Nm at 1,600-2,400 rpm
Years Fitted: 2016-2018 (W213 E-Class)

Can’t find your exact engine code?-> Get quotes for OM642 Mercedes E Class 350 d engine replacement

-> Get quotes for OM642 Mercedes E Class 350 d engine replacement

Common Problems

Mercedes E Class 350 d / 400 d Engine Problems Repair Cost vs Replacement

The E Class 350 d and 400 d represent the pinnacle of Mercedes six-cylinder diesel engineering in the W213 generation. The OM642 V6 is a proven, mature design - but carries the infamous oil cooler seal failure that has plagued this engine family for years. The later OM656 straight-six is more powerful and refined, but introduces its own set of complex issues, particularly around the integrated oil/vacuum pump. Every rebuilt engine supplied through EnginesMarket includes upgraded components designed to address the original failure point, plus a minimum 12-month unlimited mileage warranty. Below, we break down what these failures cost to fix and when replacement is the smarter option.

Common failure points and repair options

OM642 Oil Cooler Seal Failure

Affected: Mercedes E Class 350 d (OM642.853 / OM642.873, 2016-2018)
Typical failure mileage: 60,000 - 100,000 miles

Root cause

The oil cooler sits in the engine Vee and uses rubber seals that harden with heat cycles. When they fail, oil leaks into the Vee, runs down the block, and can eventually mix with coolant. The seals themselves cost as little as £5, but the labour is extensive - the intake manifold and numerous ancillaries must be removed to access them.

Repair options

Repair tier	Dealer price	Specialist price
Intermediate - Oil Cooler Seal Replacement	£1,200-£1,800	£700-£1,100
Major - Oil Cooler Seals Plus Ancillaries	£1,800-£2,500	£1,200-£1,800
Full Replacement - Rebuilt Engine	£5,500-£8,000	£3,200-£4,800

Our recommendation

If caught early with no oil-coolant emulsion, specialist seal replacement at £700-£1,100 is all you need. Once oil has blocked the turbo feed lines or emulsified coolant has damaged bearings, a rebuilt engine with upgraded seals becomes the most cost-effective long-term solution. Don't ignore oil drips under the engine bay - that's the telltale sign.

-> Compare rebuilt OM642 Mercedes E Class 350 d engine prices

OM656 Tandem Oil/Vacuum Pump Failure

Affected: Mercedes E Class 400 d (OM656.929, 2018-2023)
Typical failure mileage: 40,000 - 80,000 miles (some as early as 40k miles)

Root cause

The oil pump and vacuum pump are integrated into a single tandem unit. The seal between the oil and vacuum sides can degrade, allowing oil into the vacuum system. This compromises turbo actuator vacuum, causing intermittent limp mode, and in severe cases, complete loss of braking assistance. Early production OM656 engines (pre-2020) are more susceptible. The vacuum pipes that actuate the turbo can also collapse due to heat exposure.

Repair options

Repair tier	Dealer price	Specialist price
Intermediate - Vacuum System Diagnosis & Repair	£400-£800	£250-£500
Major - Tandem Pump Replacement	£2,500-£4,000	£1,800-£3,000
Full Replacement - Rebuilt Engine	£6,500-£10,000	£4,200-£6,500

Our recommendation

The tandem pump failure is a known design weakness on the OM656 - if your E 400 d experiences intermittent limp mode or a P0299E6 boost pressure code, get the vacuum system inspected promptly. A £250-£500 diagnosis and pipe replacement is far cheaper than the £1,800+ engine-out pump replacement. However, if the pump seal has already failed and oil has contaminated the vacuum system, the engine-out pump replacement is unavoidable. Given the £25,000+ value of most W213 E 400 d examples, this is a repair worth making.

-> Get OM656 Mercedes E Class 400 d tandem pump and turbo quotes

Timing Chain & Camshaft Wear

Affected: Mercedes E Class 400 d (OM656.929, 2018-2023)
Typical failure mileage: 80,000 - 120,000 miles

Root cause

Camshaft and rocker arm wear has been reported on OM654 and OM656 engines. The timing chain is mounted at the rear of the engine, making replacement an engine-out job. Extended oil change intervals and stop-start operation accelerate wear.

Repair options

Repair tier	Dealer price	Specialist price
Major - Camshaft & Rocker Replacement	£1,500-£2,500	£900-£1,600
Full Replacement - Rebuilt Engine	£6,500-£10,000	£4,200-£6,500

Our recommendation

Camshaft and rocker wear is a known issue on higher-mileage OM656 engines. Regular oil changes (8,000-10,000 miles) with the correct specification oil are critical to prevent premature wear. If you hear unusual top-end noise from your E 400 d, have it inspected promptly - early intervention can prevent a £4,200+ engine replacement.

-> Get OM656 Mercedes E Class 400 d camshaft replacement quotes

Don't Let Engine Failure Write Off Your Mercedes E Class 350 d or 400 d

Whether your E Class 350 d is suffering from oil cooler seal failure or your E 400 d is experiencing tandem pump issues or timing chain wear, EnginesMarket makes it simple to compare prices from trusted UK Mercedes specialists. Every rebuilt engine in our network includes upgraded components designed to address the original failure point - plus a minimum 12-month unlimited mileage warranty and nationwide delivery. Compare prices, choose a specialist, and get back on the road without the main dealer premium.

Compare Mercedes E Class 350 / 400 d Engine Replacement Prices Now ->

FAQ

Mercedes E Class 350 d / 400 d Engine ReplacementFrequently Asked Questions

Everything Mercedes Benz E Class 350 d / 400 d owners usually ask before choosing a rebuilt, reconditioned or used replacement engine.

Short summary: Supply-only rebuilt OM656 engines range from £4,200 to £6,500 depending on condition. With specialist fitting, budget £4,600-£7,300 total.

OM642.853/873 (E 350 d, 258 hp, 2016-2018): rebuilt £3,200-£4,800
OM656.929 (E 400 d, 340 hp, 2018-2023): rebuilt £4,200-£6,500
Labour adds £400-£800 depending on specialist location

-> Compare Mercedes E Class 400 d engine replacement costs by entering your reg now

Short summary: Intermittent limp mode that clears on restart, turbo actuator issues, and P0299E6 boost pressure codes are the classic signs. In severe cases, loss of braking assistance can occur.

Intermittent power loss or limp mode, clearing on engine restart
P0299E6 error code (boost pressure too low)
Juddering or clunky gear changes on longer journeys
Oil in vacuum lines (diagnostic check required)

-> Get OM656 tandem pump diagnostics before it's too late

Short summary: Yes, if the car is otherwise sound. W213 E 350 d examples command £15,000-£25,000 used, while E 400 d examples command £25,000-£40,000, making replacement viable.

A quality rebuilt OM642 costs £3,200-£4,800 supply only
A quality rebuilt OM656 costs £4,200-£6,500 supply only
The OM656 is the most powerful diesel engine Mercedes ever produced for a series car
A replacement engine with warranty costs less than the depreciation on a newer car

-> Compare rebuilt Mercedes E Class 350 / 400 d engine prices for your mileage and budget

Short summary: The rubber seals harden with heat cycles and degrade over time, causing oil to leak into the engine Vee. This is the defining weakness of the OM642 V6 engine family.

Seal failure typically occurs between 60,000-100,000 miles
Oil drips under the engine bay and a burning oil smell are the early warning signs
Oil cooler seal replacement at a specialist costs £700-£1,100
Later OM642 engines (2014+) have improved seals but can still fail

-> Get quotes for OM642 oil cooler seal replacement before it's too late

Short summary: The OM642 is a 3.0-litre V6 diesel (2016-2018 E 350 d); the OM656 is a 3.0-litre straight-six diesel (2018-2023 E 400 d) - more powerful, more refined, and borrowed from the S-Class.

OM642: V6 configuration, 258 hp, 620 Nm - proven but has oil cooler seal issues
OM656: straight-six configuration, 340 hp, 700 Nm - smoother, more powerful, but has tandem pump issues
The OM656 replaced the OM642 in the E-Class from 2018 onwards
Both are Euro 6 compliant with AdBlue emissions treatment

-> Find the correct Mercedes E Class engine for your exact chassis and engine code

Short summary: With proper maintenance and 8,000-10,000 mile oil changes, OM656 engines regularly reach 200,000+ miles. Some examples have exceeded 100,000 miles with proper servicing.

OM656 straight-six is a modern, efficient design with robust bottom end
Tandem pump replacement at 40k-80k miles is a known requirement for early examples
Camshaft and rocker inspection at 80k-100k miles is recommended
Short oil change intervals (8k miles) are critical for longevity

-> Compare Mercedes E Class 400 d engine replacement quotes - be ready when the time comes

Why Choose Us

Compare Mercedes E Class 350 / 400 d Engine Prices Today

Comparing quotes for your Mercedes E Class 350 d or 400 d engine replacement is free, no-obligation, and specific to your exact engine code and model year. Enter your registration above to get tailored prices from vetted UK specialists - whether you need a used OM642, a reconditioned OM656.929, or a fully rebuilt unit with warranty and fitting. Don't pay main dealer premiums - compare, choose, and get back on the road with confidence.

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Compare quotes from trusted UK Mercedes Benz E Class 350 d / 400 d engine specialists with warranty-backed rebuilt, reconditioned and used options nationwide.

Mercedes Benz E Class 350 d / 400 d Engine Replacement Compare Prices & Get Quotes

Get your free Mercedes Benz e-class 350 d / 400 d engine quotes

3 Simple Steps to Finding the Right Replacement Engine

Mercedes Benz E Class 350 d / 400 d Engine History & Specs at a Glance

Mercedes Benz E Class 350 d / 400 d Engine Codes Specifications & Replacement Cost

OM642.853 / OM642.873 — 3.0L V6 Diesel (2016-2018)

Mercedes E Class 350 d / 400 d Engine Problems Repair Cost vs Replacement

OM642 Oil Cooler Seal Failure

OM656 Tandem Oil/Vacuum Pump Failure

Timing Chain & Camshaft Wear

Don't Let Engine Failure Write Off Your Mercedes E Class 350 d or 400 d

Mercedes E Class 350 d / 400 d Engine ReplacementFrequently Asked Questions

Compare Mercedes E Class 350 / 400 d Engine Prices Today